Set image size in powerpoint using open xml - asp.net

Question

Im am generating a ppt-file using this tutorial here
Step 4 describes how to swap out the image placeholder.
My images has different dimensions, which makes some images look a little bit too funny.
Is there any way to resize the placeholder so it can keep the dimensions?
Edit: Ok, a better explanation: users can upload images of them selves. The images are stored on the server. I am generating a ppt-file with one user per slide. And for every slide there will be an image, if any. I can of course get the dimensions of every image, but how do I replace the placeholder with an image of another dimension than the placeholder?

Answer 1

Well, I can't tell you based on that tutorial, but I can tell you where it is done in Open XML (i.e. not the SDK).
Your picture will have an xfrm element with a set of values, like this:
<p:spPr>
<a:xfrm>
<a:off x="7048050" y="6248401"/>
<a:ext cx="972000" cy="288000"/>
</a:xfrm>
</p:spPr>
The values you want to change are the cx and cy of a:ext. Take your new picture's dimensions (h and w) from like a System.Drawing.Image object and take each of the values and multiply by 12700. So if the width of the picture is 400 pixels, the cx value of a:ext will be (400 x 12700 = 5080000).

Answer 2

This is how I did it:
using DocumentFormat.OpenXml.Packaging;
lets assume you have your SlidePart
In my case I wanted to check for the alt title of the pictures and replace them if it matches to my key.
//find all image alt title (description) in the slide
List<DocumentFormat.OpenXml.Presentation.Picture> slidePictures = slidePart.Slide.Descendants<DocumentFormat.OpenXml.Presentation.Picture>()
.Where(a => a.NonVisualPictureProperties.NonVisualDrawingProperties.Description.HasValue).Distinct().ToList();
now we check all the images:
//check all images in the slide and replace them if it matches our parameter
foreach (DocumentFormat.OpenXml.Presentation.Picture imagePlaceHolder in slidePictures)
now in the loop we look for Transform2D and modify it with our value:
Transform2D transform = imagePlaceHolder.Descendants<Transform2D>().First();
Tuple<Int64Value, Int64Value> aspectRatio = CorrectAspectRatio(param.Image.FullName, transform.Extents.Cx, transform.Extents.Cy);
transform.Extents.Cx = aspectRatio.Item1;
transform.Extents.Cy = aspectRatio.Item2;
And this function looks like this:
public static Tuple<Int64Value, Int64Value> CorrectAspectRatio(string fileName, Int64Value cx, Int64Value cy)
{
BitmapImage img = new();
using (FileStream fs = new(fileName, FileMode.Open, FileAccess.Read, FileShare.Read))
{
img.BeginInit();
img.StreamSource = fs;
img.EndInit();
}
int widthPx = img.PixelWidth;
int heightPx = img.PixelHeight;
const int EMUsPerInch = 914400;
Int64Value x = (Int64Value)(widthPx * EMUsPerInch / img.DpiX);
Int64Value y = (Int64Value)(heightPx * EMUsPerInch / img.DpiY);
if (x > cx)
{
decimal ratio = cx * 1.0m / x;
x = cx;
y = (Int64Value)(cy * ratio);
}
if (y > cy)
{
decimal ratio = cy * 1.0m / y;
y = cy;
x = (Int64Value)(cx * ratio);
}
return new Tuple<Int64Value, Int64Value>(x, y);
}
Important thing to note is that EMU per inch is 914400. In most cases you just need to divide it by 96, but for some monitors it is different. Therefore it is best to divide it the DPI for x and y.